> That's the puzzle nobody talks about: how to make a uncensorable free speech platform that's financially sustainable.

Federation is what it's called now, but back in the Old Days it was Usenet or Email or, to a lesser extent, FidoNet or any of a few other BBS UUCP-a-likes. Everyone hosts their own copies of everything, there is no central system, and there is no one to threaten if you want to remove anything.

Usenet still exists and the only ads on it are parasitic spammers. Ditto email.